Horadric Vials will also appear as rewards in chests and stashes that you open during the season. Additionally, utilizing the Whispering Tree to quickly level up your character will make these vials even more potent. The faster you progress through levels, the better the quality of Diablo IV gold the vials and other loot you receive from these chests.

How to Use Horadric Vials Wisely
Horadric Vials are used exclusively to upgrade Horadric spells, which are central to your character's power in Diablo IV. As tempting as it may be to upgrade your spells immediately, it's recommended to save your vials for later in the game. Early on, you will unlock a variety of buy D4 Gold upgradeable spell components, and it's easy to waste vials on spells that you don't end up using in the long run.